This invention relates to a method of manufacturing Josephson junctions of high Tc superconductor.
Josephson junctions being known to exhibit unique current-voltage characteristics are important elements in the field of superconducting electronics. In particular, owing to discovery of high Tc superconductors (YBa.sub.2 Cu.sub.3 O.sub.7-y) which exhibit a superconducting transition at temperatures above the boiling point of liquid nitrogen, advances are being made in research and development for utilizing Josephson junction devices, which make use of these high Tc superconductors and operate at the boiling point of liquid nitrogen, in a greater number of fields. Josephson junctions include those of the tunnel junction-type, point contact-type and bridge-type structure, and similar structures have been considered for use in high Tc superconductors. However, with the tunnel junction-type structure, the coherent length of the high Tc superconductor is short, as a result of which the thickness of the tunnel barrier is required to be made as thin as tens of angstroms. The point contact-type structure involves difficulty in terms of reproducibility and integration, while the bridge-type structure requires lift-off techniques on the submicron under. For these reasons, most Josephson junctions in the high Tc superconductors presently being developed make use of the grain boundarys of the high Tc superconductor itself, as in a micro-bridge or break junction. In order to form Josephson junctions which utilizes the grain boundary, it is necessary for the superconductor to be formed as thin films. Specifically, by employing a vacuum deposition method typified by a sputtering method or electron beam deposition method, thin films of polycrystalline high Tc superconductors are formed and the grain boundarys thereof are used to fabricate a Josephson junctions.
However, owing to the overall quality of the film, the alignment of the grain boundary present at portions other than the Josephson junction, the alignment of the grain boundary forming the Josephson junction and the precipitation of impurities at the grain boundary, the characteristics of the Josephson junctions are not satisfactory. Accordingly, the aforementioned method of manufacturing Josephson junctions are in need of improvement.